Multiple exposure photolithography methods

ABSTRACT

A method. The method forms a film of photoresist composition on a substrate and exposes a first and second region of the film to radiation through a first and second mask having a first and second image pattern, respectively. The photoresist composition includes a polymer including labile group(s), base soluble group(s), a photosensitive acid generator, and a photosensitive base generator. The photosensitive acid generator generates first and second amounts of acid upon exposure to first and second doses of radiation, respectively. The second amount of acid exceeds the first amount of acid. The second dose of radiation exceeds the first dose of radiation. The photosensitive base generator generates a first and second amount of base upon exposure to the first and second dose of radiation, respectively. The first amount of base exceeds the first amount of acid. The second amount of acid exceeds the second amount of base.

This application is a divisional application claiming priority to Ser.No. 11/970,761, filed Jan. 8, 2008.

FIELD OF THE INVENTION

The invention relates to photoresist compositions and methods forphotolithography using the same.

BACKGROUND OF THE INVENTION

Optical photolithography has been the major technique for thesemiconductor industry. Many resolution enhancement technology (RET)methods have also contributed to the extension of opticalphotolithography to print very low k1 images. The value of k₁ can befound using the optical projection lithography resolution equationW=k₁λ/NA, where W is the minimum printable feature size, λ is theexposure wavelength (e.g. 193 nm, 157 nm), NA is the numerical apertureof the lithography system and k₁ is a lithographic constant of thesystem. Double exposure (DE) has emerged as a method to reduce k₁ in thefabrication of integrated circuit chips. Several double exposure schemeshave been developed including double dipole lithography (DDL) and doubleexposure double etch (DE²). However, DDL can only print images withindiffraction limit, while DE² is a complex and expensive process.Accordingly, there exists a need to overcome the deficiencies andlimitations described hereinabove.

SUMMARY OF THE INVENTION

The present invention relates to a photoresist composition, comprising:

a polymer having a structure comprising at least one acid labile groupor at least one base soluble group;

a photosensitive acid generator capable of generating a first amount ofacid upon exposure to a first dose of radiation, said photosensitiveacid generator capable of generating a second amount of acid uponexposure to a second dose of radiation, said second amount of acidgreater than said first amount of acid, said second dose of radiationgreater than said first dose of radiation; and

a photosensitive base generator capable of generating a first amount ofbase upon exposure to said first dose of radiation, said photosensitivebase generator capable of generating a second amount of base uponexposure to said second dose of radiation, said first amount of basegreater than said first amount of acid, said second amount of base lessthan said second amount of acid.

The present invention relates to a method comprising:

forming a film of a photoresist on a substrate, said photoresistcomprising a polymer having a structure comprising at least one acidlabile group or at least one base soluble group, a photosensitive acidgenerator, and a photosensitive base generator, said photosensitive acidgenerator capable of generating a first amount of acid upon exposure toa first dose of radiation, said photosensitive acid generator capable ofgenerating a second amount of acid upon exposure to a second dose ofradiation, said second amount of acid greater than said first amount ofacid, said second dose of radiation greater than said first dose ofradiation, said photosensitive base generator capable of generating afirst amount of base upon exposure to said first dose of radiation, saidphotosensitive base generator capable of generating a second amount ofbase upon exposure to said second dose of radiation, said first amountof base greater than said first amount of acid, said second amount ofbase less than said second amount of acid;

exposing a first region of said film to radiation through a first maskhaving a first image pattern; and

exposing a second region of said film to radiation through a second maskhaving a second image pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings.

FIG. 1 is an illustration of a graph depicting an example of aphotoefficiency curve, in accordance with embodiments of the presentinvention.

FIG. 2 is an illustration of a flow chart of an example of a method forforming a patterned layer, in accordance with embodiments of the presentinvention.

FIG. 3A an illustration of a film, comprising a photoresist, disposed ona substrate, in accordance with embodiments of the present invention.

FIG. 3B is an illustration of the film of FIG. 3A being exposed toradiation, in accordance with embodiments of the present invention.

FIG. 3C is an illustration of the exposed film in FIG. 3B undergoing asecond exposure, in accordance with embodiments of the presentinvention.

FIG. 3D is an illustration of the doubly exposed film 303 in FIG. 3Cafter the film has been developed in a developer, in accordance withembodiments of the present invention.

FIG. 3E is an illustration of the doubly exposed film 303 in FIG. 3Cafter the film has been developed in a developer, in accordance withembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although certain embodiments of the present invention will be shown anddescribed in detail, it should be understood that various changes andmodifications may be made without departing from the scope of theappended claims. The scope of the present invention will in no way belimited to the number of constituting components, the materials thereof,the shapes thereof, the relative arrangement thereof, etc., and aredisclosed simply as examples of embodiments. The features and advantagesof the present invention are illustrated in detail in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout the drawings. Although the drawings are intended toillustrate the present invention, the drawings are not necessarily drawnto scale.

The photoresist composition described herein may comprise a polymer, aphotosensitive acid generator, and a photosensitive base generator. Thepolymer of the photoresist described herein may comprise any polymersuitable for chemically amplified photoresists. The polymer may have astructure comprising at least one acid labile group or at least one basesoluble group. For example, a polymer in a positive tone chemicallyamplified system may comprise at least one repeating unit having atleast one acid labile group which can be deprotected in anacid-catalyzed thermal baking process making the polymer substantiallysoluble in base developers. In another example, a polymer in a negativetone chemically amplified system may comprise at least one repeatingunit having at least one base soluble group which may allow the polymerto be substantially soluble in base developers. The polymer may beconfigured to crosslink or undergo a polarity change in anacid-catalyzed thermal baking process, thus making the polymersubstantially insoluble in base developers. The polymer of thephotoresist may comprise a homopolymer, a copolymer, a terpolymer, atetrapolymer, etc. The polymer may comprise a polymer blend of two ormore polymers, such as blends of two or more of the polymers describedabove. In some embodiments, the polymer structure may comprise repeatingunits such as:

The photoresist composition may comprise a photosensitive base generator(PBG). A photosensitive base generator is a compound which produces abase upon exposure to a dose of electromagnetic radiation, such asvisible, ultraviolet (UV) and extreme ultraviolet (EUV), for example.Some suitable photosensitive base generators may produce an amine baseupon exposure to radiation.

Some examples of suitable photosensitive base generators include: benzylcarbamates of the structure

where R¹=H or alkyl group, R²=alkyl, substituted alkyl, aryl orsubstituted aryl group, R³, R⁴═H, alkyl, substituted alkyl, aryl orsubstituted aryl group, and R⁵=aryl group, R¹ and R² may link to form acyclic structure, such as 2-nitrobenzyl carbamates where R⁵ is a2-nitrophenyl group and R³, R⁴═H; Carbamates of the structure

where R¹=H or alkyl group, R²=alkyl, substituted alkyl, aryl orsubstituted aryl group, R¹ and R² may link to form a cyclic structure,and R³=alkyl, substituted alkyl, aryl or substituted aryl group;Benzoin carbamates (2-oxo-1,2-diphenylthyl carbamates) of the structure

where R¹═H or alkyl group, R²=alkyl, substituted alkyl, aryl orsubstituted aryl group, R¹ and R² may link to form a cyclic structure,and R⁵ and R⁶ may each independently be an aryl or a substituted arylgroup, such as benzoin carbamates where R¹=H, R²═C₆ to C₁₀ alkyl group,andR⁵ and R⁶ are each phenyl groups;O-carbamoylhydroxylamines of the structure

where R¹═H or alkyl group; R²=alkyl, substituted alkyl, aryl orsubstituted aryl group, R¹ and R² may link to form a cyclic structure,and R³, R⁴═H, alkyl, substituted alkyl, aryl, substituted aryl, or acylgroup, such as O-carbamolhydroxphthalamides where R¹═H, R²═C₆ to C₁₀alkyl group, and R³ and R⁴ are each a 2-carboxybenzoyl group;O-Carbamoyloximes of the structure

where R¹═H or alkyl group, R²=alkyl or aryl group, and R³, R⁴═H, alkyl,substituted alkyl, aryl, or substituted aryl group; Aromaticsulfonamides of the structure

where R¹═H or alkyl group, R²=alkyl, substituted alkyl, aryl orsubstituted aryl group, R¹ and R² may link to form a cyclic structure,and R³=aryl group or substituted aryl groups;α-Lactones of the structure

where R²=alkyl, aryl group, R³=alkyl, substituted alkyl, aryl, orsubstituted aryl group;

-   N-(2-Arylethenyl)amides of the structure

where R³=alkyl, substituted alkyl, aryl, or substituted aryl group,R⁴=alkyl or substituted alkyl group, and R⁵=aryl group; Azides of thestructure

R⁶N₃

where R⁶=aryl or substituted aryl group;Amides of the structure

where R⁶=aryl or substituted aryl group, R⁷═H, alkyl, substituted alkyl,aryl or substituted aryl group;Oximines of the structure

where R³, R⁴, R⁸=alkyl, substituted alkyl, aryl or substituted arylgroup;Quaternary ammonium salts of the structure

where R³, R⁴, R⁸, R⁹=alkyl, substituted alkyl, aryl or substituted arylgroup, A⁻=an anion such as a halide ion (such as Cl⁻, BR⁻, I⁻, F⁻, etc.)or sulfonate ion; and

Amineimides of the structure

Where each of R³, R⁴, R⁸ and R⁹ is an alkyl, substituted alkyl, aryl orsubstituted aryl group, In all the above structural formulas: R¹ is H,an alkyl group or a substituted alkyl group; and R² is an alkyl group,substituted alkyl group, an aromatic group, or an substituted aromaticgroup. The PBG described above may also be linked to form dimers, wheresuch a linkage may prevent volatility of the base produced.

Polymeric materials incorporating the compounds described above may alsobe useful as photosensitive base generators. Polyurethanes are examplesof such polymers.

Other examples of suitable photosensitive base generators within thescope of the photoresist composition described herein includecarbamates, such as:

The photoresist may comprise a photosensitive acid generator (PAG),capable of releasing or generating an amount of acid (such as 1 mole ofacid per mole of PAG, for example) upon exposure to a dose ofelectromagnetic radiation, such as visible, ultraviolet (UV) and extremeultraviolet (EUV), for example. The PAG may comprise, for example,triphenyl sulfonium nonaflate (TPSN),(trifluoro-methylsulfonyloxy)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide(MDT), N-hydroxy-naphthalimide (DDSN), onium salts, aromatic diazoniumsalts, sulfonium salts, diaryliodonium salts, sulfonic acid esters ofN-hydroxyamides, imides, or combinations thereof.

Photosensitive acid generators and photosensitive base generators asused herein may each be described as having a photoefficiency, wherephotoefficiency may be described as the amount of acid or base,respectively, produced per dose of radiation at a particular wavelengthor over a range of wavelengths. Compounds having low photoefficienciesrequire higher doses of radiation to produce the same amount of acid orbase as compounds having higher photoefficiencies.

A photoefficiency may be determined for a particular PAG or PBG bytitrating the acid or base produced in a resist composition afterexposure to a particular dose of radiation. A series of titrations atdifferent concentrations of PAG or PBG through a range of exposure dosesmay be used to produce a photoefficiency curve representing acid or baseproduction as a function of radiation dose. The radiation dose range maybe from 0 millijoules/(centimeter) (mj/cm²) to about 100 mj/cm², forexample. Titrations may be performed using methods known in the art suchas with indicators and an appropriate base or acid, where indicatorconcentrations may be determined using known methods such as UV-visspectroscopy, for example. For example, a known amount of PAG or PBG maybe incorporated into a photoresist formulation having an amount of anappropriate indicator (i.e. a specific indicator for an acid or base).The decrease in the concentration of indicator may then be determinedfor each dose of radiation to which a sample (such as a film) of thephotoresist is exposed, where the decrease in indicator concentration isequal to the increase in acid or base produced by the PAG or PBG,respectively. In some embodiments, the same indicator may be used forboth acid titration and base titration. For example, for an acidindicator, the concentration of the indicator decreases with an increasein the radiation dose exposed to the PAG. The same indicator may be usedfor determining base generation by a PBG, by first reacting theindicator with a known quantity of acid, followed by exposure to aradiation dose. In this case, the concentration of the indicatorincreases with the increase in radiation dose exposed to the PBG.

In embodiments of the photoresist described herein comprising a polymer,a PBG, and a PAG, the PBG may have a higher photoefficiency than thePAG. Thus at low radiation doses, the PBG may produce base in higherconcentration than the acid produced by an equivalent amount of the PAGat the same radiation dose. The higher concentration of base producedthan acid equates to a higher amount of PBG consumed (to produce thebase) than the amount of PAG consumed (to produce the acid). Atsufficiently high radiation doses, the PAG may produce the sameconcentration of acid as the concentration of base produced by the PBGat the same higher dose, such as a dose where PBG and PAG areessentially completely consumed.

In some embodiments of the photoresists herein, the concentration of PAGin the resist may be higher that the concentration of PBG in the resist.For such a resist composition, the ratio of the concentrations of PAG toPBG may be such that at low radiation doses, the concentration of baseproduced by the PBG may be greater that the concentration of acidproduced by the PAG, whereas for higher doses of radiation, theconcentration of acid produced by the PAG may be greater than theconcentration of base produced by the PBG.

FIG. 1 is an illustration of a graph depicting an example of aphotoefficiency curve for a PBG 100 and a theoretical photoefficiencycurve for a PAG 105, where acid and base concentration are plotted as afunction of radiation dose. In this example, the concentration of PAG ishigher than the concentration of PBG in the resist. In a range of lowradiation dose 110, the curve for the PBG 100 is higher than the curvefor the PAG 105 indicating the photoefficiency of the PBG issufficiently high to produce sufficient base to neutralize all of theacid produced by the PAG. Whereas in a range of high radiation dose 115,the PAG curve 105 is higher than the curve for the PBG 110, indicatingthat the PAG produces a higher concentration of acid than theconcentration of base produced by the PBG. The ratio of concentrationsof the PAG and the PBG may be varied to provide a desired amount ofexcess base in the low dose range and excess acid in the high doserange. For example, a smaller ratio of PAG to PBG may reduce the amountof excess acid in the high dose range, and may increase the amount ofexcess base in the low dose range. Likewise, adjusting the relativeamounts of PAG and PBG in a photoresist formulation may allow for makingchanges in the amount of base and acid produced in regions receivinghigh doses of radiation and low dose of radiation.

The compositions and relative concentrations of PBG and PAG may each beselected based on photoefficiency curves of each such that a “crossoverpoint” is present such as point 120 in FIG. 1, above which theconcentration of acid produced exceeds the concentration of baseproduced, and below which the concentration of base produced exceeds theconcentration of acid produced. For example, the PAG may be selectedsuch that the PAG is capable of generating a first amount of acid uponexposure to a first dose of radiation, and capable of generating asecond amount of acid upon exposure to a second dose of radiation, wherethe second amount of acid is greater than the first amount of acid, andthe second dose of radiation is greater than first dose of radiation.Likewise, the PBG may be selected such that the PBG is capable ofgenerating a first amount of base upon exposure to the same first doseof radiation as the PAG, and capable of generating a second amount ofbase upon exposure to the same second dose of radiation as the PAG,where the first amount of base is greater than the first amount of acid,and the second amount of base is less than the second amount of acid.

A film of the photoresist described above regarding FIG. 1, when exposedto radiation (such as being patternwise imaged though a mask), wheresome regions of the film are exposed to radiation and other regions ofthe film are unexposed, some regions may be exposed to low doses ofradiation such as regions near or between boundaries of exposed regionsand unexposed regions. Some low dose regions and high dose regions maythus be adjacent and contiguous with each other, where the high and lowdose regions may be connected in a continuous mode. The terms high doseand low dose indicate the regions exposed to high and low relativeradiation dose ranges, respectively, such as described for high and lowdose ranges 115 and 110, respectively, of FIG. 1. The dose distributionmay be determined by the aerial images projected on the resist film. Forexample, in high contrast images, the low dose regions are narrow.Conversely, for low contrast images, the low dose regions are broad. Lowradiation doses in boundary regions are caused by phenomena such asdiffraction of the radiation (such as electromagnetic radiation) passingthrough transparent narrow openings (unmasked areas) in the mask. Inregions of the film exposed to low doses of radiation (low doseregions), the base produced by the PBG may be in sufficient excess toneutralize essentially all of the acid produced by the PAG in the lowdose region and allow for some of the produced base to remain in the lowdose region. Likewise, in regions of the photoresist film exposed tohigher doses of radiation (high dose region), such as in exposed areasnot near boundaries, the acid produced by the PAG may be in sufficientexcess to neutralize essentially all of the base produced by the PBG inthe high dose region and to allow for some of the produced acid toremain in the high dose region, where the acid may react with thepolymer of the composition. Thus in the low dose exposed regions of thephotoresist, acid produced as a result of radiation exposure isneutralized and is prevented from affecting the resist formulation, suchas reacting with the polymer of the resist Likewise, in high doseexposed regions of the photoresist, base produced by the PBG as a resultof radiation exposure is neutralized by the acid produced by the PAG,where the acid may be in sufficient excess to affect the resistformulation, such as by reaction with the polymer to make itsubstantially soluble or substantially insoluble in a developerdepending upon the polymer composition.

The photoresist may further comprise a base proliferator, where a baseproliferator is a compound capable of producing an amount of basethrough catalytic reaction with another base. For example, the baseproliferator may be capable of releasing base through a base-catalyzeddecomposition mechanism, thus the base proliferator may initiate acascade of reactions to form a large amount of base. The baseproliferation process may be triggered by heat in combination with acatalytic amount of base. The presence of a base proliferator mayamplify the effects of the PBG when exposed to radiation such as whenpatternwise imaging a resist film as described above. Thus baseconcentrations remaining in low dose regions of the resist afterexposure to radiation may be amplified or increased by reaction with abase proliferator present in the resist formulation in the low doseregion.

Some examples of base proliferators include fluorenylmethyl carbamates,phenylsulfonylethyl carbamates, and 3-nitropentane-2-yl carbamates, suchas:

wherein each R¹ or R² is independently selected from the groupconsisting of a hydrogen atom, a linear alkyl, a branched alkyl, acycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, ahalogenated cycloalkyl, an aryl, a halogenated aryl, and combinationsthereof, and wherein R⁴ may be hydrogen or alkyl. Halogenated maycomprise fluorinated, chlorinated, or brominated. For example, each R¹or R² may be independently selected from the group consisting of afluorinated linear alkyl, a fluorinated branched alkyl, a fluorinatedcycloalkyl, an aryl, a fluorinated aryl, and combinations thereof,wherein R³ is selected from the group consisting of a fluorinated linearalkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl,a fluorinated aryl, and combinations thereof.

The base proliferators described above may also be linked to form dimerstructures, where such linking may prevent volatility of the baseproduced. Some examples of dimer forms of base proliferators include:

wherein each R¹ or R² is independently selected from the groupconsisting of a hydrogen atom, a linear alkyl, a branched alkyl, acycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, ahalogenated cycloalkyl, an aryl, a halogenated aryl, and combinationsthereof, wherein R³ is selected from the group consisting of a linearalkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, ahalogenated branched alkyl, a halogenated cycloalkyl, an aryl, ahalogenated aryl, and combinations thereof, and wherein R⁴ may behydrogen or alkyl. As above, halogenated may comprise fluorinated,chlorinated, or brominated. For example, each R¹ or R² may beindependently selected from the group consisting of a fluorinated linearalkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl,a fluorinated aryl, and combinations thereof, wherein R³ is selectedfrom the group consisting of a fluorinated linear alkyl, a fluorinatedbranched alkyl, a fluorinated cycloalkyl, an aryl, a fluorinated aryl,and combinations thereof.

The photoresist may further comprise a surfactant. Surfactants may beused to improve coating uniformity, and may include ionic, non-ionic,monomeric, oligomeric, and polymeric species, or combinations thereof.Examples of possible surfactants include fluorine-containing surfactantssuch as the FLUORAD series available from 3M Company in St. Paul, Minn.,and siloxane-containing surfactants such as the SILWET series availablefrom Union Carbide Corporation in Danbury, Conn.

The photoresist may include a casting solvent to dissolve the othercomponents, so that the photoresist may be applied evenly on thesubstrate surface to provide a defect-free coating. Where thephotoresist is used in a multilayer imaging process, the solvent used inthe imaging layer may not be a solvent to the underlayer materials,otherwise unwanted intermixing may occur. Some examples of suitablecasting solvents include ethers, glycol ethers, aromatic hydrocarbons,ketones, esters, ethyl lactate, gamma-butyrolactone (GBL),cyclohexanone, ethoxyethylpropionate (EEP), a combination of EEP andGBL, and propylene glycol methyl ether acetate (PGMEA). The presentinvention is not limited to the selection of any particular solvent.

The photoresist may include a base quencher, sensitizers or otherexpedients known in the art. The compositions of the photoresistsdescribed herein are not limited to any specific selection of theseexpedients, where base quenchers may comprise aliphatic amines, aromaticamines, carboxylates, hydroxides, or combinations thereof. For examplebase quenchers may include: dimethylamino pyridine,7-diethylamino-4-methyl coumarin (Coumarin 1), tertiary amines,sterically hindered diamine and guanidine bases such as1,8-bis(dimethylamino)naphthalene (PROTON SPONGE), berberine, orpolymeric amines such as in the PLURONIC or TETRONIC series commerciallyavailable from BASF. Tetra alkyl ammonium hydroxides or cetyltrimethylammonium hydroxide may be used as a base quencher when the PAG is anonium salt. For photoresist embodiments comprising a base proliferator,quenchers may comprise weak base quenchers or those quenchers havingamine groups protected with acid labile groups, such as t-butyl groups.

The photoresist composition is not limited to any specific proportionsof the various components. The photoresist composition may compriseabout 1% by weight (wt %) to about 30 wt % of polymer based on the totalweight of the composition, such as from about 2 wt % to about 15 wt %.The photoresist composition may comprise from about 0.1 wt % to about 30wt % photosensitive base generator based on the weight of the polymer inthe composition, such as from about 0.1 wt % to about 20 wt %. Thephotoresist composition may comprise from about 0.5 wt % to about 30 wt% photosensitive acid generator based on the weight of the polymer inthe composition, such as from about 0.5 wt % to about 20 wt %. Thephotoresist composition may comprise from about 0.1 wt % to about 30 wt% base proliferator based on the weight of the polymer in thecomposition, such as from about 0.1 wt % to about 20 wt %. Thephotoresist composition may comprise from about 70 wt % to about 99 wt.% solvent based on the total weight of the composition, such as fromabout 85 wt % to about 98 wt %. The photoresist composition may furtherinclude about 0.1 wt % to about 1.0 wt % of base quencher based on thetotal weight of the polymer in the composition. The photoresistcomposition may further include about 0.001 wt % to about 0.1 wt % ofsurfactant based on the total weight of polymer in the composition.

The term substantially insoluble, as used herein, is intended tocomprise having such a small degree of solubility so as to not effectthe quality of an image formed from a photoresist by loss of material(e.g. polymer, photoresist, etc.) through dissolution into aqueous basesolution or photoresist solvents from regions of the photoresist layernot containing photosensitive acid generator derived acid. The termsubstantially soluble, as used herein, is intended to comprise having ahigh enough degree of solubility in aqueous base solutions or solventsso to allow all or almost all (i.e., any remaining material is presentsuch a small amounts so as to not interfere with subsequent processingsteps) of the material (e.g. polymer, photoresist, etc.) in regionscontaining acid derived from the photosensitive acid generator todissolve into aqueous base solutions or photoresist solvents. In thecontext of photoresist formulation and semiconductor processing the termsubstantially insoluble is intended to include polymers completely oralmost completely insoluble in photoresist solvents. In the context ofphotoresist formulation and semiconductor processing the termsubstantially soluble is intended to include polymers completely oralmost completely soluble in photoresist solvents. In general, thepolymer dissolution rates affect the dissolution rates of thephotoresist layers most strongly, thus a substantially insoluble polymermay render substantially insoluble a photoresist comprising thatpolymer. Substantially insoluble photoresists have a dissolution rate ofless than about 0.2 nanometers/second (nm/s) in solvent or aqueous base,while substantially soluble photoresists have a dissolution rate ofgreater than about 5 nm/s in solvent or aqueous base. Photosensitiveacid generators, quencher and other additives may also alter thedissolution rates of the final photoresist layer.

FIG. 2 is an illustration of a flow chart of an example of a method forforming a patterned layer. Step 210 comprises forming a film of aphotoresist on a substrate, where the photoresist composition maycomprise a polymer, a PAG, and a PBG, such as described above. In thephotoresist composition, the concentration of the PAG may be higher thanthe concentration of the PBG. The polymer may have a structurecomprising at least one acid labile group or at least one base solublegroup. The PAG may be capable of generating a first amount of acid uponexposure to a first dose of radiation, and capable of generating asecond amount of acid upon exposure to a second dose of radiation, wherethe second amount of acid is greater than the first amount of acid, andthe second dose of radiation is greater than said first dose ofradiation. The PBG generator may be capable of generating a first amountof base upon exposure to the same first dose of radiation (for example,the same magnitude and wavelength of radiation), and capable ofgenerating a second amount of base upon exposure to the same second doseof radiation, where the first amount of base is greater than the firstamount of acid (i.e. base is in excess of acid), and the second amountof base is less than the second amount of acid (i.e. the acid is inexcess of base). An example of this is described above wherephotoefficiency curves of the acid and base have a crossover point asillustrated in FIG. 1.

The film may be formed by a process such as spin coating, spray coating,dip coating, doctor-blading, roll coating, and the like, which may beused individually or in one or more combination thereof in accordancewith the methods of the present invention. The substrate may comprisematerials of one or more of the IUPAC Groups 4, 6, 11, 12, 13, 14, and15 elements, plastic material, silicon dioxide, glass, fused silica,mica, ceramic, metals deposited on the aforementioned substrates,combinations thereof, and the like. The substrate may comprise a stackor layering of different materials. For a substrate used in a trilayerapproach, there may be a comparatively thick organic underlayer and athin Si containing interlayer, where the Si containing layer may eitherbe a chemical vapor deposited silicon oxide layer or a spin coatedsilsesquioxane polymer film. For example, a substrate may comprise aprepared silicon wafer substrate such as those employed in semiconductormanufacturing. The films and layers described herein may be disposed ontop of the substrate or may be integrally joined with the substrate.

Step 215 comprises exposing a first region of the film to radiationhaving a first exposure dose, resulting in the photosensitive acidgenerator generating a first acid catalyst in the exposed first regionof the film and the photosensitive base generator generating a firstbase in the exposed first region of the film, where the exposed firstregion comprises a first low dose region and a first high dose region.

A high dose region, as described herein, comprises a portion of anexposed region receiving radiation of sufficiently high dosage such thatthe amount of acid generated by the PAG is greater than the amount ofbase generated by the PBG, such as the high radiation dose range 115 inFIG. 1. A low dose region, as described herein, comprises a portion ofan exposed region receiving radiation of sufficiently low dosage suchthat the amount of base generated by the PBG is greater than the amountof acid generated by the PAG, such as the low radiation dose range 110in FIG. 1. For example, in a first portion of the exposed region theconcentration of the acid catalyst is higher than the concentration ofthe base (such as in high dose regions), and in a second portion of theexposed region the concentration of the acid catalyst is lower than theconcentration of the base (such as in low dose regions).

As a result of exposing the film to radiation, as described herein, thefilm may comprise a plurality of exposed regions, each comprising aplurality of low dose regions and a plurality of high dose regions,where each low dose region is included in the plurality of low doseregions, and each high dose region is included in the plurality of highdose regions.

The first base may be in sufficient excess of the first acid catalyst inthe first low dose region such that a first portion of the first baseneutralizes essentially all of the first acid catalyst in the first lowdose region and a second portion of the first base remains in the firstlow dose region. For example, the boundary areas between the firstexposed region and unexposed regions of the film may be a low doseregion, such as an exposed boundary area as described above, where thePBG generates an amount of base in excess of acid catalyst generated bythe PAG, such as is illustrated in FIG. 1.

The first acid catalyst may be in sufficient excess of the first base inthe first high dose region such that a first portion of the first acidneutralizes essentially all of the first base in the first high doseregion and a second portion of the first acid catalyst remains in thefirst high dose region. For example, areas of the first exposed regionnear the center of the exposed area, away from boundary areas may behigh dose regions. The remaining portion of the first acid catalyst mayinteract with the polymer of the photoresist, such as by crosslinking oracid catalyzed bond cleavage.

Step 220 comprises exposing a second region of the film to radiationhaving a second exposure dose, resulting in the photosensitive acidgenerator generating a second acid catalyst in the exposed second regionof the film and the photosensitive base generator generating a secondbase in the exposed second region of the film, where the exposed secondregion comprises a second low dose region and a second high dose region.

The first exposure dose and the second exposure dose may be equal ordifferent. For example, the first exposure dose may be higher or lowerthan the first exposure dose depending on the formulation of the resistand the process steps applied before the second exposure.

The second base may be in sufficient excess of the second acid catalystin the second low dose region such that a first portion of the secondbase neutralizes essentially all of the second acid catalyst in thesecond low dose region and a second portion of the second base remainsin the second low dose region. For example, the boundary areas betweenthe second exposed region and unexposed regions of the film may be a lowdose region, such as an exposed boundary area as described above, wherethe PBG generates an amount of base in excess of acid catalyst generatedby the PAG, such as is illustrated in FIG. 1.

The second acid catalyst may be in sufficient excess of the second basein the second high dose region such that a first portion of the secondacid neutralizes essentially all of the second base in the second highdose region and a second portion of the second acid catalyst remains inthe second high dose region. For example, areas of the second exposedregion near the center of the exposed area, away from boundary areas maybe high dose regions. The remaining portion of the second acid in thehigh dose region may interact with the polymer of the photoresist, suchas by crosslinking or acid catalyzed bond cleavage.

Exposing the first region of the film to radiation in step 215 maycomprise patternwise imaging the film through a first mask having afirst image pattern. Exposing the second region of the first film toradiation in step 220 may comprise patternwise imaging the film througha second mask having a second image pattern. The first image pattern maybe different or the same as the second image pattern. Resulting frompatternwise imaging the film through the first mask and patternwiseimaging the film through the second mask, at least one area of the filmmay remain unexposed to the radiation and a second region of the filmmay be exposed to the radiation. For example, the first and second imagepatterns may each have sections essentially transparent to theradiation, and each may have sections essentially opaque to theradiation. The transparent and opaque areas of each image pattern may ormay not coincide, such that after the first and second exposures, theremay be areas of the film which remain unexposed to radiation. Likewise,there may be regions of the film which have been exposed through thefirst image pattern, the second image pattern, or both.

The exposed regions of the film may comprise the first region exposed insteps 215 and the second region exposed in step 220. In someembodiments, one of the exposed first regions may be adjacent to orcontiguous with one of the second exposed regions (e.g. the firstexposed region and the second exposed region share an edge or boundary).Excess base in overlapping low dose areas (such as the boundary areasnear the edges of these exposed regions) prevents the first and secondexposed regions from overlapping their acid distribution with eachother, resulting in improving the resolution of the double exposedpatterns from the two exposures, by neutralizing acid catalyst in thelow dose areas between the two exposed regions and preventing the acidcatalyst from reacting with the polymer of the photoresist. Theincorporation of base proliferator in the resist formulation may enhancethe base concentration in the boundary areas through base proliferation,such as through baking at elevated temperature. Therefore, a baking stepmay be used between step 215 and 220 when the resist composition furthercomprises a base proliferator. For example, after the patternwiseimaging of the film and before the developing of the film, the resistfilm may be baked at a temperature between about 80° C. and about 150°C.

Referring again to FIG. 2, the method may further comprise step 225,step 225 comprising removing soluble portions of the film, afterexposing the second region, to leave a patterned layer remaining, wherethe patterned layer has a photoresist pattern. For example, removingsoluble portions of the film may comprise developing the film in anaqueous base solution where the base-soluble exposed regions (orunexposed region for a negative tone resist) of the film may be removedfrom the film to form a patterned layer of the photoresist film. Thedeveloper may be organic or aqueous based, such as an aqueous basedeveloper such as tetramethylammonium hydroxide (TMAH) aqueous solution,for example.

FIG. 3A is an illustration of a film 303, comprising a photoresist,disposed on a substrate 300, such as the photoresist films andsubstrates described above. FIG. 3B is an illustration of the film 303of FIG. 3A being exposed to radiation as described for step 215 of FIG.2, wherein a first radiation source 310 projects radiation through afirst patterned mask 315 onto the film 303 disposed on the substrate300. The first mask 315 may have a first image pattern comprising maskedsections 320, which are essentially opaque to the radiation, andunmasked sections 325, which are essentially transparent to theradiation. Radiation passing through the unmasked sections 325 may betransmitted to the film 303 and simultaneously be received and absorbedin high dose region 330 and adjacent low dose regions 335 of the film303. The dose of radiation in the high dose region 330 may be in a rangeof high radiation dosage, such as the high radiation dose range 115illustrated in FIG. 1. The dose of radiation received by the low doseregion 335 may be in a range of low radiation dosage, such as the lowradiation dose range 110 of FIG. 1. The film may comprise unexposedareas 305 after the first exposure to radiation. The radiation mayinduce the production of an acid catalyst by the PAG in the exposedregions 330 and 335 of the film 303, where unexposed areas 305 of film303 may not produce an acid catalyst. The radiation may induce theproduction of base by the PBG in the exposed regions 330 and 335, wherein low dose regions 335 the produced base may be in higher concentrationthan acid and may neutralize essentially all the acid catalyst producedin the low dose regions 335. In the high dose regions 330, the acidcatalyst produced by the PAG may be in higher concentration than thebase produced by the PBG and thus the acid in the high dose region mayneutralize essentially all of the base in the high dose region 330.Sufficient acid catalyst may remain in the high dose regions 330 afterreaction with the base to interact with the polymer of the photoresist,such as by crosslinking or acid catalyzed bond cleavage.

FIG. 3C is an illustration of the exposed film 303 in FIG. 3B undergoinga second exposure, wherein a second radiation source 345 projectsradiation through a second patterned mask 350 onto the film 303 disposedon a substrate 300. As a result of the second exposure, the film mayfurther comprise exposed regions 337 and 365, where 365 may be a highdose region and adjacent region 337 may be a low dose region, such as isdescribed above. At least one area 305 of the film 303 may remainunexposed after the first and second exposures. At least one low doseregion 335 and at least one low dose region 337 may overlap to form anoverlap area 339 between two adjacent exposed regions. The PAG mayproduce an acid catalyst in the high dose region 335 and the low doseregion 337, where the acid produced in the low dose region 337 by thePAG may be essentially neutralized by base produced in the low doseregion 337 by the PBG as a result of the second exposure to radiation.Base produced by the PBG in the high dose region 365 may be essentiallyneutralized by a portion of the acid produced in sufficient excess inthe high dose region 365 by the PAG such that a portion of the acidremains and may react with the polymer of the photoresist. The excessbase produced in the overlap area 339 neutralizes acid catalyst in theoverlap area 339 thus preventing interaction of the acid catalyst withthe polymer of the photoresist in the overlap area 339.

The photoresist may comprise a negative tone photoresist, where thepolymer may be configured such that, as a result of the first and secondexposures, unexposed areas 305, low dose regions 335 and 337, andoverlap region 339 may be removed in a developing step comprisingdeveloping the film 303 in a developer (such as aqueous base orsolvent), where the unexposed areas 305, low dose regions 335 and 337,and overlap region 339 of the film 303 are base-soluble regions. Such apolymer configuration may comprise base-soluble groups in the polymerstructure, where acid catalyst reaction with the polymer in the highdose regions 330 and 365 may render the polymer insoluble in aqueousbase developer. For example, the polymer in the high dose regions 330and 365 may undergo crosslinking and become insoluble in developer.

The photoresist may comprise a positive tone photoresists, where thepolymer may be configured such that, as a result of the first and secondexposures, exposed regions of the film 303 may be removed in adeveloping step comprising developing the film in a developer (such asaqueous base or solvent), where the exposed regions of the film arebase-soluble, such as where acid catalyst reacts with the polymer (suchas high dose regions 365 and 330). Such a polymer configuration maycomprise a polymer structure having acid labile groups which may becleaved by reaction with the acid catalyst, thus rendering the polymersoluble in developer.

After the patternwise imaging of the film and before developing, thefilm may be baked at a temperature between about 80° C. and about 150°C.

FIG. 3D is an illustration of the doubly exposed film 303 in FIG. 3Cafter the film has been developed in a developer (such as aqueous base)and, as a result of the developing, unexposed areas 305 and low doseregions 335, 337 and 339 of the film 303 have been removed and a firstpatterned layer 380 of the film 303 is formed. The first patterned layermay have a photoresist pattern comprising features 370 and 375 remainingon the surface of the substrate 300, where features 370 and 375 areformed from exposed high dose regions 365 and 330, respectively. In theexample of FIG. 3D, the polymer composition was such that the acidcatalyst produced in the exposed areas 365 and 330 of FIG. 3C interactedwith the polymer in such a way as to render the polymer in those areasinsoluble in developer such that the unexposed areas 305 and low doseregions 335, 337 and 339 in FIG. 3C were removed to leave the firstpatterned layer 380 remaining.

FIG. 3E is an illustration of the doubly exposed film 303 in FIG. 3Cafter the film has been developed in a developer (such as aqueous base)and, as a result of the developing, exposed high dose regions 330 and365 of the film 303 have been removed and a second patterned layer 395of the film 303 is formed. The second patterned layer 395 may have aphotoresist pattern comprising features 396, 398, and 397 remaining onthe surface of the substrate 300, as well as open gaps 385 and 390 wheregaps 385 and 390 are open areas remaining after the removal of exposedhigh dose regions 330 and 365, respectively. In the example of FIG. 3E,the polymer composition was such that the acid catalyst produced in theexposed high dose regions 365 and 330 of FIG. 3C interacted with thepolymer in such a way as to render the polymer in those regions solublein developer such that the exposed high dose regions 365 and 330 wereremoved, leaving unexposed areas 305 and low dose regions 335, 337 and339 to leave the patterned layer 395 remaining.

The photoresist pattern of the patterned layer may be transferred to thesubstrate. If the substrate comprises an antireflective coating (ARC)and/or planarizing underlayer onto which the photoresist film has beenformed, the ARC and/or planarizing underlayer may be removed at the gapsin the patterned photoresist layer to expose portions of the substrate.For example, the antireflective coating and/or planarizing underlayermay be removed by etching. Once the desired portions of the substrateare exposed, the photoresist pattern in the patterned layer (e.g. thepattern of gaps within the exposed film) may be transferred to portionsof the substrate. Transferring the pattern may comprise, for example,etching, such as reactive ion etching (RIE), depositing (such as vapordeposition or electroplating) a material (such as a dielectric, a metal,a ceramic or a semiconductor) onto the substrate in a gap in the exposedphotoresist film, by implanting dopants into the substrate material in agap in the exposed photresist film, or by a combination of one or moreof these methods.

The photoresists and films thereof described herein may be patternwiseimaged using radiation such as ultraviolet (UV) such as wavelengths ofapproximately 436 nanometers (nm) and 365 nm, deep-ultraviolet (DUV)such as wavelengths of approximately 257 nm, 248 nm, 193 nm, and 157 nm,extreme-ultraviolet (EUV) such as a wavelength of approximately 4 nm toapproximately 70 nm such as approximately 13 nm, x-ray, combinations ofthese, and the like. Various wavelengths of radiation may be used suchas 313 nm, 334 nm, 405 nm, and 126 nm etc., where the sources may bemainly from specific mercury emission lines or specific lasers. For highperformance lithography, single wavelength and/or narrow band radiationsources may be used. For less stringent conditions, a broad bandmultiple wavelength source may be used. The photoresist compositions ofthe present invention may be patternwise imaged using particle beamssuch as electron beam, ion beam, combinations of these, and the like.The appropriate radiation or particle beam type(s) may depend on thecomponents of the overall photoresist composition (e.g., the selectionof the PBG, polymer, photosensitive acid generator (PAG), baseproliferator, base (or quencher), surfactant, solvent, etc.).

Example 1

A terpolymer comprising 45 mole % MAdMA, 15 mole % STAR and 40 mole %NLM was dissolved in PGMEA with 4 wt % TPSN (triphenyl sulfoniumnonaflate), 0.85 weight % (wt %) (i.e. 20 mole %) of DNC and 0.93 wt %(i.e. 20 mole %) of DFC (all wt. % are relative to total polymer weight)to make a solution having 7 wt % of solid content. The resultingsolution was filtered through a 0.2 micron (μm) filter. The resist wasspin coated onto a 12 inch silicon wafer which had an approximately 42nanometer (nm) thickness coating of Rohm & Haas bottom anti-reflectivecoating (BARC) named AR40A. The resist was post-applying baked (PAB) atabout 110° C. for about 60 seconds and exposed to 193 nm wavelengthlight on an ASML stepper (1.1 NA, 0.75 outer and 0.55 inner σ annularillumination). The wafer was then post-exposure baked (PEB) at about120° C. for about 60 seconds. The film was developed using a singlepuddle develop process for about 30 seconds with 0.263 N TMAH(tetramethylammonium hydroxide) developer (Moses Lake's AD-10). At thedose of 14.8 millijoules/centimeter² (mj/cm²), the 85 nm lines on a 180nm pitch were resolved.

Example 2

A terpolymer comprising 45 mole % MAdMA, 15 mole % STAR and 40 mole %NLM was dissolved in PGMEA with 4 wt % TPSN (triphenyl sulfoniumnonaflate), 0.40 wt % (i.e. 20 mole %) of NBC-101 and 0.93 wt % (20 mole%) of DFC (all wt. % are relative to total polymer weight) to make asolution having 7 wt % of solid content. The resulting solution wasfiltered through a 0.2 μm filter. The resist was spin coated onto a 12inch silicon wafer which had an approximately 42 nm thickness coating ofRohm & Haas bottom anti-reflective coating (BARC) named AR40A. Theresist was post-applying baked (PAB) at about 110° C. for about 60seconds and exposed to 193 nm wavelength light on an ASML stepper (1.1NA, 0.75 outer and 0.55 inner σ annular illumination). The wafer wasthen post-exposure baked (PEB) at about 120° C. for about 60 seconds.The film was then developed using a single puddle develop process forabout 30 seconds with 0.263 N TMAH developer (Moses Lake's AD-10). Atthe dose of 14.8 mj/cm2, the 85 nm lines on a 180 nm pitch wereresolved.

Example 3

A terpolymer ccomprising 45 mole % MAdMA, 15 mole % STAR and 40 mole %NLM was dissolved in PGMEA with 4 wt % TPSN (triphenyl sulfoniumnonaflate), 0.14 wt % (i.e. 5 mole %) of ANC and 0.93 wt % (i.e. 20 mole%) of DFC (all wt. % are relative to total polymer weight) to make asolution with about 7 wt % of solid content. The resulting solution wasfiltered through a 0.2 μm filter. The resist was spin coated onto a 12inch silicon wafer which had an approximate 42 nm thickness coating ofRohm & Haas bottom anti-reflective coating (BARC) named AR40A. Theresist was post-applying baked (PAB) at about 110° C. for about 60seconds and exposed to 193 nm wavelength light on an ASML stepper (1.1NA, 0.75 outer and 0.55 inner σannular illumination). The wafer was thenpost-exposure baked (PEB) at about 120° C. for about 60 seconds. Thefilm was developed using a single puddle develop process for about 30seconds with 0.263 N TMAH developer (Moses Lake's AD-10). At the dose of14.8 mj/cm2, 85 nm lines on a 180 nm pitch were resolved.

The foregoing description of the embodiments of this invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to aperson skilled in the art are intended to be included within the scopeof this invention as defined by the accompanying claims.

1. A method comprising: forming a film of a photoresist composition on a substrate, said photoresist composition comprising a polymer having a structure comprising at least one acid labile group or at least one base soluble group, a photosensitive acid generator, and a photosensitive base generator, said photosensitive acid generator capable of generating a first amount of acid upon exposure to a first dose of radiation, said photosensitive acid generator capable of generating a second amount of acid upon exposure to a second dose of radiation, said second amount of acid greater than said first amount of acid, said second dose of radiation greater than said first dose of radiation, said photosensitive base generator capable of generating a first amount of base upon exposure to said first dose of radiation, said photosensitive base generator capable of generating a second amount of base upon exposure to said second dose of radiation, said first amount of base greater than said first amount of acid, said second amount of base less than said second amount of acid; exposing a first region of said film to radiation through a first mask having a first image pattern; and exposing a second region of said film to radiation through a second mask having a second image pattern.
 2. The method of claim 1, said method further comprising, after said exposing said first region of said film to radiation, generating, by said photosensitive acid generator, a first acid catalyst in said exposed first region of said film and generating, by said photosensitive base generator, a first base in said exposed first region of said film, wherein a first concentration of said first acid catalyst in a first portion of said exposed first region is higher than a first concentration of said first base in said first portion of said exposed first region, wherein a second concentration of said acid catalyst in a second portion of said exposed first region is lower than a second concentration of said first base in said second portion of said exposed first region.
 3. The method of claim 1, said method further comprising after said exposing said second region, baking said film at a temperature between about 80° C. and about 150° C.; and after said exposing said first region and before said exposing said second region, baking said film at a temperature between about 80° C. and about 150° C.
 4. The method of claim 1, wherein said first image pattern is different from said second image pattern.
 5. The method of claim 1, said method further comprising after said exposing said second region, removing soluble portions of said film to leave a patterned layer remaining, said patterned layer having a photoresist pattern.
 6. The method of claim 5, said method further comprising: after said removing said soluble portions of said film, transferring said photoresist pattern from said patterned layer to said substrate, said transferring comprising a method selected from the group consisting of depositing, implanting, electroplating, etching and combinations thereof.
 7. The method of claim 1, wherein said photoresist composition comprises a higher concentration of said photosensitive acid generator than said photosensitive base generator.
 8. The method of claim 1, wherein said photosensitive acid generator is selected from the group consisting of (trifluoro-methylsulfonyloxy)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide (MDT), N-hydroxy-naphthalimide (DDSN), onium salts, aromatic diazonium salts, sulfonium salts, diaryliodonium salts, sulfonic acid esters of N-hydroxyamides, imides, and combinations thereof.
 9. The method of claim 1, wherein said photosensitive base generator is selected from the group consisting of carbamates, benzyl carbamates, benzoin carbamates, O-carbamoylhydroxylamines, O-carbamoyloximes, aromatic sulfonamides, α-lactones, N-(2-Arylethenyl)amides, azides, amides, oximines, quaternary ammonium salts, and amineimides.
 10. The method of claim 1, wherein said photosensitive base generator is a carbamate selected from the group consisting of:


11. The method of claim 1, said photoresist composition further comprising a base proliferator, said base proliferator comprising a compound capable of generating a second base through catalytic reaction with said first base.
 12. The method of claim 11, wherein said base proliferator is selected from the group consisting of fluorenylmethyl carbamates, phenylsulfonylethyl carbamates, and 3-nitropentane-2-yl carbamates.
 13. The method of claim 11, wherein said base proliferator is selected from the group consisting of:

wherein each R¹ or R² is independently selected from the group consisting of a hydrogen atom, a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R³ is selected from the group consisting of a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R⁴ is hydrogen or alkyl.
 14. The method of claim 13, wherein each R¹, R², or R³ further comprises at least one element selected from the group consisting of oxygen, sulfur, and nitrogen.
 15. The method of claim 13, wherein each R¹ or R² is independently selected from the group consisting of a fluorinated linear alkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl, a fluorinated aryl, and combinations thereof, wherein R³ is selected from the group consisting of a fluorinated linear alkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl, a fluorinated aryl, and combinations thereof.
 16. The method of claim 1, wherein said photosensitive base generator is a carbamate consisting of:


17. The method of claim 1, said photoresist composition further comprising a base proliferator, said base proliferator comprising a compound capable of generating a second base through catalytic reaction with said first base, wherein said base proliferator is selected from the group consisting of 3-nitropentane-2-yl carbamates.
 18. The method of claim 1, said photoresist composition further comprising a base proliferator, said base proliferator comprising a compound capable of generating a second base through catalytic reaction with said first base, wherein said base proliferator is selected from the group consisting of:

wherein each R¹ or R² is independently selected from the group consisting of a hydrogen atom, a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R³ is selected from the group consisting of a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R⁴ is hydrogen or alkyl, wherein each R¹, R², or R³ further comprises at least one element selected from the group consisting of oxygen, sulfur, and nitrogen.
 19. The method of claim 1, said photoresist composition further comprising a base proliferator, said base proliferator comprising a compound capable of generating a second base through catalytic reaction with said first base, wherein said base proliferator is selected from the group consisting of:

wherein each R¹ or R² is independently selected from the group consisting of a hydrogen atom, a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R³ is selected from the group consisting of a linear alkyl, a branched alkyl, a cycloalkyl, a halogenated linear alkyl, a halogenated branched alkyl, a halogenated cycloalkyl, an aryl, a halogenated aryl, and combinations thereof, wherein R⁴ is hydrogen or alkyl, wherein each R¹ or R² is independently selected from the group consisting of a fluorinated linear alkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl, a fluorinated aryl, and combinations thereof, wherein R³ is selected from the group consisting of a fluorinated linear alkyl, a fluorinated branched alkyl, a fluorinated cycloalkyl, an aryl, a fluorinated aryl, and combinations thereof. 